Table Of ContentGenesis and Properties of Collapsible Soils
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Series C: Mathematical and Physical Sciences - Vol. 468
Genesis and Properties
of Collapsible Soils
edited by
Edward Derbyshire (Editor-in-Chief )
Department of Geography,
Royal Holloway, University of London,
Egham, Surrey, U.K.
Tom Dijkstr a
and
Ian J. Smalley
Centre for Loess Research,
Department of Civil Engineering,
Loughborough University of Technology,
Loughborough, U.K.
Springer Science+Business Media, B.V.
Proceedings of the NATO Advanced Research Workshop on
Genesis and Properties of Collapsible Soils
Loughborough, U.K.
11-14 April 1994
A C.I.P. Catalogue record for this book is available from the Library of Congress
ISBN 978-94-010-4047-1 ISBN 978-94-011-0097-7 (eBook)
DOI 10.1007/978-94-011-0097-7
Printed on acid-free paper
All Rights Reserved
© 1995 Springer Science+Business Media Dordrecht
Originally published by Kluwer Academic Publishers in 1995
Softcover reprint of the hardcover 1st edition 1995
No part of the material protected by this copyright notice may be reproduced or
utilized in any form or by any means, electronic or mechanical, including photo
copying, recording or by any information storage and retrieval system, without written
permission from the copyright owner.
TABLE OF CONTENTS
Preface vii
Types and Distribution ofCollapsible Soils
C.D.F. Rogers
Six DefinableParticleTypes in Engineering Soils and TheirParticipation in Collapse
Events: Proposals and Discussions
I. Jefferson and I.,J. Smalley 19
A Stress Path Model for CollapsibleLoess
R.L. Handy 33
Factors and Mechanism ofLoess Collapsibility
V.I. Osipov and V.N. Sokolov 49
Techniques to Examine Microfabric and Particle Interaction ofCollapsible Soils
N.K. Tovey 65
On the Development ofMicrostructure in Collapsible Soils
J. Locat 93
The Slovak Carpathians Loess Sediments, TheirFabric and Properties
A. Klukanova and J. Frankovska 129
Mechanisms ofCollapse ofSoil Structure
~F~a 1@
The Collapse Mechanism ofa Soil Subjected to One-Dimensional Loading and Wetting
D.G. Fredlund and J.K.M. Gan 173
TheInfluence ofthe Clay Componentin Loess on Collapse ofthe Soil Structure
T.W. Mellors 207
Interpretation and Comparison ofCollapse Measurement Techniques
S.L. Houston, W.N. Houston and H.H. Mahmoud 217
Consideration ofthe Possible Contributions ofAmorphous Phases to the Sensitivity of
Glaciomarine Clays
S.P. Bentley and A.J. Roberts 225
Variation in Collapsibility and Strength ofLoess with Age
Z. Lin 247
Collapsible Loess on the Loess Plateau ofChina
E. Derbyshire, X. Meng, J.T. Wang, Z. Zhou and B. Li 267
vi
Post-Depositional Processes in High-Sensitivity, Fine-Grained, Collapsible Sediments
J.K. Torrance 295
Changes in WaterChemistry and Loess Porosity with Leaching: Implications for
Collapsibility in the Loess ofNorth China
T. Muxart, A. Billard, A. Andrieu, E. Derbyshire and X. Meng 313
Effects ofRock Fragments on the Structural Collapse ofTilled Topsoils During Rain
J.W.A. Poesen and B. Van Wesemael 333
Simulation and Modelling ofCollapsible Soils
J.D. Nieuwenhuis and M.B. de Groot 345
Collapse Mechanisms and Design Considerations for Some Partly Saturated and Saturated
Soils
G. Lefebvre 361
Design and Treatment ofLoess Bases in Bulgaria
D. Evstatiev 375
Comparison ofResults ofOedometer and Plate Load Tests Performed on Collapsible Soils
Y.M. Reznik 383
Post-script 409
Index 411
PREFACE
Soil collapse forms a major hazard in large parts ofeastern Canada, the United States, eastern
Europe,ChinaandsouthernAfrica.Thesedimentsinvolvedincludeyoung marineclaysand lake
sediments,wind-depositedmaterials(loessandsomesands),volcanicash,andsomeresidualsoils.
Humanactivitiescontinuetoincreaseinregionsunderlainbycollapsiblesoils,sothatthehazards
posed are increasing in both relative and absolute terms. The purpose ofthe NATO Advanced
Research Workshop held in Loughborough, England, was to bring together international
researchers from several scientific fields (civil engineering, engineering geology, stratigraphy,
geomorphology and soil science) that have generally lacked close interaction in addressing this
particularprobleminthepast.Theaim was to identifygoalsinthestudyofthe collapseprocess,
to propose mutually-acceptable working definitions of "collapse", and to formulate collapse
models as a key to soil treatment so as to enhance utilisation and diminish hazard.
Collapsiblesoilsare metastable. Agranular material withangularparticles compactedonthe
dry side of optimum can form a structure which is capable of further densification. This is a
phenomenon known from the full particle size range - from clays to coarse rock aggregates.
However, the classic collapsible soils are natural materials in which particle type and
sedimentation mechanism combine to produce collapsibility. The collapsing soils problem is
exacerbated by a paucity ofdescriptive terms.
Collapsiblesoilhasarelativelylowhorizontal-to-verticalstressratioKothatrelatestoelastic
deformationandPoisson'sratio, and collapseinvolvingsaturationleads to aliquidorhydrostatic
stressconditionwhereby Ko = 1.0.Recentyears haveseenamajoradvance in thequantification
ofsoil microfabric, particularly using image processing and analysis techniques. From a micro
mechanical viewpoint, collapse occurs by de-bonding, grain crushing, fabric transition, and by
temporarykinematicconstraint.Inthemacromechanicalsenseitoccursbyloading,wetting,creep,
radialsoftening,andbyexcessporewaterpressures.Soilsasastructuredsystembehaveasallsuch
systems: gradual (smooth) development (deformation) is periodically interrupted by collapse
events.Inloess,thecollapsephenomenonoccursthroughmicro-shearingatintergranularcontacts,
and is influenced by the clay component: it may be explained in terms ofa modified effective
stress equation.
LoessofPleistoceneageisthemostwidelydistributedcollapsiblesoil.Mostobservedchanges
initsmechanicalpropertiesaretheresultofpost-depositionalprocesses,reflectingtheweathering
andpedogenesisofthelast3millionyears. However, changewithage(depth) ismuchless than
with climatic gradient, as in North China. Here "initial collapsepressure" and "preconsolidation
pressure" of saturated samples are technical synonyms. Multiple buried soils are an important
sourceofvariation in bulk properties as well as some importantcauses ofvariation in the mode
offailure and the collapse potential.
Post-depositional processes may both aggravate and alleviate collapse problems in several
types ofsediment. Theconsequences ofcollapse are usually moreserious in materials with high
sensitivity. Developmentofhighsensitivityis usuallyapost-depositionalprocessarisingfrom (i)
decreaseoftheremoulded strength, and (b) increaseofthe undisturbedstrength. Sensitivity may
bedecreased by weatheringordiageneticprocesseswhichproduceswellingclaymineralsand/or
oxidemineralsand/oragents which increaseparticleinteraction indisturbed material. The fabric
ofcollapsiblesoilscanbecharacterisedusingmicromorphologicaltechniques,thesebeingauseful
aid in explaining and predicting collapse.
The collapse mechanisms may be modelled mathematically. In the case of subaqueous
flowslides, comparisons between quantitative simulations and field observations highlight the
vii
viii
influence ofsoil density, slope angle and slope height. Causes and mechanisms ofcollapse can
be specified for different soil types including soft sensitive clays, loose unsaturated orsaturated
sandsorsilty sands,and loess. Althoughdifferentindetail, the behaviourofthesedifferentsoils
has manycommonfeatures andrequiresquitesimilarapproachestodesign. Forstabilityanalysis,
theshearstrengthparametersmustbedefinedforthepost-collapseconditiononceanequilibrium
has developed between effective stress, voids ratio, and shear stress. The advantages and
limitationsofanumberofremedialstrategiestominimisecollapseinloess werediscussed in the
final open session in Loughborough.
TheWorkshopconcludedwithanew workingdefmitionofsoilcollapsewhichemphasisethe
structural strengthofthe grain skeleton as aunifying factor. Given thatcollapse is the transition
from an open metastable packing to a closer, more stable packing, then the open structure of
quickclays, loess and sands is a unifying entity. Regional views of the collapsibility of loess
clearly emerged during the Workshop: eastern European, Chinese and North American, in
particular. The main communication "gap" appears to lie between the micromorphologists (soil
scientists) and the remainder. Strategies for future research into the collapse phenomenon were
discussed and some broad avenues agreed. Longer-tenn research objectives requiring
interdisciplinary collaboration also emerged. It was agreed by the group that, in future, special
attention will begiven to (1)detennininganddescribingsoilandsedimentstructures; (2)finding
waystodetenninechangesinstructure;(3)improvingmineralogicaldescription;and(4)mapping
collapsible soils.
This volume contains 21 ofthe 27 papers presented at the Loughborough meeting. As the
Director of the Workshop, I am acutely aware of the debt of gratitude lowe to a number of
organisationsandindividuals.First,IampleasedtoacknowledgetheScientificandEnvironmental
Affairs DivisionoftheNorth AtlanticTreatyOrganisation whosecontractualgrantARW931148
provided the means of organisation the meeting and compiling this book. I would like, in
particular,tothankLuigiSertorio,fonnerDirectoroftheARWProgrammeforhisencouragement
and support in the early days oforganising this event. Special thanks are also due to Drs. Tom
Dijkstra for his very practical help immediately before and during the Workshop, to Meng
Xingmin and Justin Jacyno for computercartography, and to Kathy Roberts at Royal Holloway
(University of London) for exceeding the secretarial speed limit and withstanding deadline
pressures without complaint. Itis a pleasure to thank ourcolleagues in the Department ofCivil
and Building Engineering ofLoughborough University ofTechnology for making all workshop
contributors so welcome. Maryon Derbyshirestoically tookontheonerous taskofcompilingthe
index, and my co-editors Tom Dijkstra and Ian Smalley are gratefully acknowledged for their
influenceonthewaytheWorkshopwasshapedandfortheirevaluationofearlyversionsofsome
papers.Finally,Iwarmlyapplaudthedistinguished,livelyandgood-humouredgroupofscientists
who, by theirprofessionalism, made this meetingamostrewarding intellectualexperience. They
were the Workshop, and they made the book. It is dedicated to them.
Edward Derbyshire
Editor-in-Chief
March 1995
MainirrigationpiperupturedbysubsidenceinhighlycollapsibleloessonGaolan
Mountain,Lanzhou, north-centralChina.
TYPES ANDDISTRIBUTIONOFCOLLAPSmLESOILS
C.D.F. ROGERS
SeniorLecturerinGeotechnics
DepartmentofCivilandBuildingEngineering
LoughboroughUniversityofTechnology
Leicestershire, UnitedKingdom
ABSTRACT. Collapsiblesoilsaremetastableandmusthavean open structure,that isthesoil
particles must be in an open packing which is capable of becoming a (significantly) closer
packing. Agranularmaterial withangularparticles compactedonthedry sideofoptimum can
form astructurewhich iscapableofsignificantfurther densification, buttheclassic collapsible
soilsarenaturalmaterialswherethecombinationofparticletypeandsedimentationmechanism
combinetogivecollapsibility. Thereisafiercedebateaboutwhatsoilsshouldbeconsideredas
collapsible and this has spawned several definitions ofa collapsible soil, all ofwhich are in
some way limiting. The debate is advanced hereafter by consideration, from a geotechnical
viewpoint, of what is not a collapsible soil. Thereafter a simple hierarchical, systematic
classification can be produced which allows both compacted and natural materials to be
included. Ageographicalclassificationwhichplacesalltypesofnatural collapsiblesystemson
a convenient base map is also required. This paper aims to address both ofthese issues by
consideringcollapsiblesoilsintheirwidestpossiblesense.
1. Introduction
This paper was written primarily to form a good starting point for discussions on the
genesis and properties ofcollapsible soils, the paper constitutingthe first keynote talk
toa NATOworkshoponthistopic [I). Theaimofthepaperwas toproduce a critique,
from a geotechnical engineering viewpoint, of the various attempts to classify
collapsible soilsinorderthat the typesofcollapsible soil encountered in practice could
bedefined. Inconsideringthevarioustypesofcollapsiblesoil that occurit is necessary
to consider the genesis ofthese soils, which results in turn in a consideration ofthe
distributionofthe majordepositsofcollapsiblesoilsworldWide.
In order to meet these primary aims, it was important that collapsible soils should
be considered in their widest sense. It rapidly became clear that the subject is one
which is addressed by researchers from numerous academic disciplines ranging from
geotechnical engineers through engineering geologists, geologists, geomorphologists
andsedimentologiststo soil scientists. It is necessarily the casethat the boundaries of
study ofthese disciplines will limit the subject definition and that each will form a
subsetofthewhole. Itequallybecameapparentthatgeotechnical engineeringprovided
the bestvantage point from which to view these various subsets since it must become
involved, at some point, in all natural and man-made soils. Nevertheless full
1
E.Derbyshireeta1.(eds.),GenesisandPropertiesofCollapsibleSoils, 1-17.
©1995KluwerAcademicPublishers.
